Commit message: Ensure non-empty rt_nested_splits in tf.raw_ops.RaggedTensorToVariant

PiperOrigin-RevId: 387664237
Change-Id: Ia1700c34b5610873d63561abc86e23b46ead93b3
CVE: CVE-2021-37666
CWE: CWE-125
Vulnerability description: TensorFlow is an end-to-end open source platform for machine learning. In affected versions an attacker can cause undefined behavior via binding a reference to null pointer in `tf.raw_ops.RaggedTensorToVariant`. The [implementation](https://github.com/tensorflow/tensorflow/blob/460e000de3a83278fb00b61a16d161b1964f15f4/tensorflow/core/kernels/ragged_tensor_to_variant_op.cc#L129) has an incomplete validation of the splits values, missing the case when the argument would be empty. We have patched the issue in GitHub commit be7a4de6adfbd303ce08be4332554dff70362612. The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, as these are also affected and still in supported range.

Project: tensorflow
File: ragged_tensor_to_variant_op.cc

  void Compute(OpKernelContext* context) override {
    // Read ragged_splits inputs.
    OpInputList ragged_nested_splits_in;
    OP_REQUIRES_OK(context, context->input_list("rt_nested_splits",
                                                &ragged_nested_splits_in));
    const int ragged_nested_splits_len = ragged_nested_splits_in.size();
    RaggedTensorVariant batched_ragged_input;
    // Read ragged_values input.
    batched_ragged_input.set_values(context->input(ragged_nested_splits_len));
    batched_ragged_input.mutable_nested_splits()->reserve(
        ragged_nested_splits_len);
    for (int i = 0; i < ragged_nested_splits_len; i++) {
      batched_ragged_input.append_splits(ragged_nested_splits_in[i]);
    }

    if (!batched_input_) {
      // Encode as a Scalar Variant Tensor.
      Tensor* encoded_scalar;
      OP_REQUIRES_OK(context, context->allocate_output(0, TensorShape({}),
                                                       &encoded_scalar));
      encoded_scalar->scalar<Variant>()() = std::move(batched_ragged_input);
      return;
    }

    // Checked here instead of at input in case batched_input_ is false
    OP_REQUIRES(context, ragged_nested_splits_len > 0,
                errors::InvalidArgument(
                    "rt_nested_splits must be a list of one or more, but "
                    "received rt_nested_splits of length 0."));

    // Unbatch the Ragged Tensor and encode the components.
    std::vector<RaggedTensorVariant> unbatched_ragged_input;
    auto batched_splits_top_vec =
        batched_ragged_input.splits(0).vec<SPLIT_TYPE>();
    int num_components = batched_splits_top_vec.size() - 1;
    OP_REQUIRES(context, num_components >= 0,
                errors::Internal("Invalid split argument."));
    OP_REQUIRES_OK(context, UnbatchRaggedZerothDim<VALUE_TYPE, SPLIT_TYPE>(
                                batched_ragged_input, &unbatched_ragged_input));

    // Bundle the encoded scalar Variant Tensors into a rank-1 Variant Tensor.
    Tensor* encoded_vector;
    int output_size = unbatched_ragged_input.size();
    OP_REQUIRES_OK(context,
                   context->allocate_output(0, TensorShape({output_size}),
                                            &encoded_vector));
    auto encoded_vector_t = encoded_vector->vec<Variant>();
    for (int i = 0; i < output_size; i++) {
      encoded_vector_t(i) = unbatched_ragged_input[i];
    }
  }